PASADENA, Calif. — After a journey of 354 million miles to the outskirts of Mars, the Curiosity rover and its spacecraft are speeding up and coming under the influence of the planet’s gravity as it prepares for a dramatic landing early Monday.

NASA officials said early Sunday afternoon that the spacecraft was about 100,000 miles from Mars and remained in ideal shape. They also said its position in relation to the point selected to enter the atmosphere also is on target. The upcoming landing is one of the riskiest ever tried, with final descent that starts at 13,200 mph and ends after what NASA officials call “seven minutes of terror.”

That landing is scheduled for 1:31 a.m., and officials said they could know almost immediately if the rover was safely on the ground. That tracking would come from the Odyssey orbiter circling Mars, if the spacecraft is able to get to the right location at the right time.

If not, the waiting time for a final answer on whether the rover was safely on the surface could range from two to eight hours. If no signal arrives from Curiosity via three Mars orbiters and the Deep Space Network after 18 hours, NASA officials said, then they would start to worry about its safety.

The final descent has been pre-programmed and the army of engineers and scientists at the Jet Propulsion Lab’s Mission Control have no control over it. “Our position will be identical to anyone at home,” said Adam Steltzner, lead of the Entry, Descent and Landing (EDL) team. “We’re all along for the ride.”

Speaking for the team as a whole, Steltzner said they were “Rationally confident, emotionally terrified and ready for EDL.”

Because the rover is so much larger, more complicated and more ambitious than earlier models, it has to land in a new and far more hazardous way. The landing, which could never be tested in full on Earth, includes a hovering rocket stage, a kind of sky crane, to lower it to the ground. NASA’s chief scientist John Grunsfeld has said that because of that heightened landing difficulty, in addition to the unprecedented sophistication of the instruments on board, Curiosity is “the most important NASA mission of the decade.”

Worldwide spectacle

The Curiosity landing is shaping up to be an international spectacle. Formal “landing” parties have been scheduled from South Australia to Rome, from Israel to Crete; and in the United States from Atlanta to Seattle, Milwaukee to Honolulu.

NASA also has helped organize a landing gathering in New York’s Times Square, which will feature a large screen that will beam the streaming news from atop a building and high above the crowd.

Reaching, orbiting and landing on Mars is notoriously hard. In addition to the European Space Agency, nations including the United States, the former Soviet Union, Russia, the European Space Agency, China and Japan have sent missions to Mars since the late 1960s, but only about one-third of them have succeeded.

The United States is the only nation to land a vehicle on Mars and complete its mission, having done it six out of seven tries.

The Soviet Union was the first to touch down on the Martian surface, but that 1971 mission ended 14 seconds later when all communication ceased.

NASA’s confidence in the mission is reflected in the aggressive way it’s trying to bring it to the public, from landing-based X-box games to those many parties.

But reflecting the ever-present possibility of failure, Mars Exploration program director Doug McQuiston said: “If we’re not successful, we will have learned from it. We’ll pick ourselves up, dust ourselves off and do it again.”

The first Mars pictures expected from Curiosity will be relatively primitive fish-eye black-and-white images that will have been transmitted either within the first few minutes after touchdown or two hours later, when the orbiting Odyssey satellite again passes over the landing site.

Higher-resolution and color images from other cameras could come later in the week, and a video filmed of the last minute of the landing from the vehicle will be released weeks later, because it will take longer to download.

Ambitious mission

Curiosity is not only the most expensive and ambitious mission ever sent to another planet, but it also has a formal goal unattempted by NASA since the Viking landers of the mid-1970s: a search for the building blocks of extraterrestrial life. The rover carries three chemistry labs that will search for carbon-based organic material and Martian habitats where life once may have flourished.

An army of 700 engineers and scientists is converging at the Jet Propulsion Lab to watch and tweak the landing, and then to hopefully begin the slow process of getting the rover ready for operations.

The earliest tests will begin within a day of landing, but moving, digging soil and drilling rocks won’t take place for weeks or months, agency officials said.

Curiosity is the first rover to land any place on Mars other than a flat plain. Because of advances in landing technology, it will touch down instead in Gale Crater, a large and ancient hole in the ground about three miles deep.

At its center is Mount Sharp — named after California Institute of Technology planetary scientist Robert Sharp — which will offer geologists and planetary scientists their first opportunity to observe and analyze the history of the planet as laid down in its exposed rock layers.

Temperatures in the crater are expected to range from 10 degrees during the day to 100 degrees below zero at night. The rover has a nuclear-powered battery that it uses to create the heat needed to keep the rover from freezing and the electricity to move its wheels and to operate its 10 instruments.

As the landing approaches, a potentially disruptive dust storm in southern Mars being monitored by NASA’s Mars Reconnaissance Orbiter appears to be dissipating, according to JPL’s Ashwin Vasavada, deputy project scientist for Curiosity. “Mars is cooperating by providing good weather for landing.”

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